Studies of Li intercalation of hydrogenated graphene on SiC(0001)
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چکیده
The effects of Li deposition on hydrogenated bilayer graphene on SiC(0001) samples, i.e. on quasi-freestanding bilayer graphene samples is studied using low energy electron microscopy, micro-low-energy electron diffraction and photoelectron spectroscopy. After deposition, some Li atoms form islands on the surface creating defects that are observed to disappear after annealing. Some other Li atoms are found to penetrate through the bilayer graphene sample and into the interface where H already resides. This is revealed by the existence of shifted components, related to H-SiC and Li-SiC bonding, in recorded core level spectra. The Dirac point is found to exhibit a rigid shift to about 1.25 eV below the Fermi level, indicating strong electron doping of the graphene by the deposited Li. After annealing the sample at 300-400 oC formation of LiH at the interface is suggested from the observed change of the dipole layer at the interface. Annealing at 600 oC or higher removes both Li and H from the sample and a monolayer graphene sample is reestablished. The Li thus promotes the removal of H from the interface at a considerably lower temperature than after pure H intercalation. Introduction Graphene has attracted intense recent interest due to its unique two-dimensional electron gas and electron transport properties [1-3]. This makes graphene a promising material for future carbon-based electronic devices. Epitaxial growth of graphene on silicon carbide (SiC) was proposed as the way to fabricate high quality graphene with a large homogeneous area [4-6]. In addition, the epitaxial growth on the Si-terminated SiC(0001) substrate is known to allow preparation of large homogeneous graphene samples with a thickness down to a single monolayer [4-5, 7]. On the C-terminated SiC(000 1 ) substrate [8] it has been difficult to control the number of graphene layers. However, for epitaxial
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تاریخ انتشار 2012